1. Field of the Invention
This invention relates to a transmission changeover mechanism for a camera using a planetary gear.
2. Description of the Related Art
In the past, operating mechanisms in a camera, for example, the film transportion mechanism, or the charging mechanism for the shutter, have been driven by the driving power of a motor. It is known that a planetary clutch is arranged between this operating mechanism and the aforesaid motor in order to change the gear ratio or to selectively operate a plurality of operating mechanisms depending on the direction of rotation of the motor. The above-defined planetary clutch comprises a sun gear connected to is driven by the gear. Depending on the normal or reverse rotation of the sun gear, the planetary gear is brought into or taken out of engagement with a gear to be driven, as it revolves round the sun gear. This function is utilized in changing over the transmission system.
In FIG. 1 there is shown the conventional transmission changeover mechanism in the form of the planetary clutch incorporated to the operating mechanism in the camera. When the sun gear 50 rotates in the counterclockwise direction indicated by the arrow, a planetary carrier or lever 54, because it is frictionally connected to the sun gear 50, turns in the counterclockwise direction until the planetary gear 52 engages a 2-stage gear 60. A small gear of this 2-stage gear 60 always meshes with a drive gear 8 on which is formed a charge cam 9. Therefore, rotation of the planetary gear 52 is transmitted to the drive gear 8. By the clockwise rotation of the cam 9, a power storing lever 10 is turned in a counterclockwise direction to move a charge lever 20 in such a direction that power is stored on a drive spring (not shown) for the shutter or the like.
Here, the direction of power transmission from the planetary gear 52 to the 2-stage gear 60 coincides with the meshing pressure angle direction (indicated by arrow B). When the sun gear 50 is driven as the motion generating wheel, therefore, if the planetary gear 52 and the 2-stage gear 60 are once engaged with each other, the engagement is never broken during the driving opertion. However, even if the direction of rotation of the sun gear 50 is the arrow direction (counterclockwise direction), when the power transmission changes its direction to: the 2-stage gear 60.fwdarw. the planetary gear 52.fwdarw. the sun gear 50, in other words, when the 2-stage gear 60 is driven to rotate at a faster speed than that of rotation of the planetary gear 52, the power transfer across the tooth surfaces occurs in a direction indicated by arrow D, expelling the planetary gear 52 out of engagement.
Actually, in case the charging of the camera is performed through the above-described planetary clutch, it is customary that the mechanism to be driven, such as the mirror mechanism or shutter is arranged to be charged by the reciprocating lever 10 in such a manner that the charge lever 20 is urged to store power on the drive spring therefor, and, when the operating mechanism is actuated, for example, the shutter operation terminates, the charge lever 20 returns to the initial position. That is, when the charge cam 9 is rotated in the clockwise direction by the motor (not shown) through the planetary clutch, the power storing lever 10 turns in the counterclockwise direction to perform charging of the camera. FIG. 1 illustrates the initial stage of the aforesaid charging, and FIG. 2 illustrates a stage near (just before) the end of charge angle. In this charging operation, the active force F of the power storing lever 10 works, except for the state of FIG. 2, so as to turn the charge cam 9 in the counterclockwise direction. But, when the state of FIG. 2 is reached, the active force F of the power storing lever 10 works so as to turn the charge cam 9 in the reverse or clockwise direction by the cam displacement of the charge cam 9. For this reason, it is near the end of the charging of the camera that the load of the side to be driven (the active force F) backs up the charge cam 9 in the driving direction, whereby the direction of transmission of the drrving power is reversed. Therefore, the planetary gear 52 has a force applied so that it tends to disengage from the 2-stage gear 60. As a result, the operative connection between the charge cam 9 and the sun gear 50 is cut off, and the control to insure that the cam 9 is made to stop in a prescribed position becomes impossible, permitting it to overrun which causes the power storing lever 10 to slightly turn in the charging direction again. If, in this state, the camera is actuated, the charge lever 20 which would normally move to the position indicated by dashed lines in FIG. 2, because of the power storing lever 10 being not fully retracted, collides with the power strong lever on the way and is stopped. For this reason, a faulty operation of the camera occurs, and the possibility of damaging the operating mechanism is increased.